Apart from its direct impact on human health, diet also indirectly modulates health through its interaction with the human gut microbiome. The largest emphasis is placed on the role of indigestible dietary glycans, insoluble dietary fiber in particular, as driver of microbiome dynamics, composition and functionality. Here, we investigated how human gut derived microbiota respond to dietary shifts on the short term (hours) and long term (days) and what impact this yields in terms of microbiome resilience against antibiotic stressors. Our experimental design of choice was SHIME®, a dynamic model of the human gut, as it allows the study of different gut regions (proximal vs. distal colon, mucus vs. gut lumen) with a multiparametric control of dietary and digestive parameters on human microbiota from the same biological background. Subjecting human gut microbiota to wheat bran as insoluble dietary fiber revealed a rapid and dynamic response over a 72h timeframe with an initial enrichment of Enterobacteriaceae and Fusobacterium species, preferentially growing on proteinaceous substrate in the medium. The onset of wheat bran fermentation, marked by a spike in short chain fatty acid production with an increasing butyrate proportion and an increased endo-1,4-β-xylanase activity, corresponded to donor-dependent proportional increases of Bacteroides ovatus/stercoris, Prevotella copri and Firmicutes species, which were strongly enriched in the bran-attached community. Over a longer timeframe we found insoluble wheat bran to serve as an adhesion platform for Lactobacillus, Bifidobacterium and Dialister species, Roseburia faecis, Prevotella copri and Bacteroides ovatus and to upregulate the functional niches of propionate- and butyrate-producing, particularly in the proximal colon. Moreover, a wheat bran conditioned microbiota also displayed higher resilience against an imposed antibiotic stress with maintenance of microbiota homeostasis and a faster recovery of propionate functionality. This unprecedented time-resolved analysis sheds more light on how insoluble dietary fiber not only facilitates the production of health-related fermentation metabolites but also yields a stabilizing effect keeping the microbial ecosystem further away from a dysbiotic tipping point.

Wheat bran as insoluble dietary fiber drives human gut microbiome stability and functionality

ACS Fall 2021

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